In recent years, miniaturization/weight reduction and multifunctionalization of electronic instruments represented by cellular phones have been rapidly progressed. As properties required for an internal wiring material of the electronic instruments as described above, there are mentioned: that the internal wiring material should have a thin diameter; that the internal wiring material should be excellent in shielding properties; that the internal wiring material should be capable of high-speed signal transfer; and the like. Moreover, among the cellular phones, those have been increased, in each of which a cabinet on an LCD screen side and a cabinet on a main board side are connected to each other through a hinge. For such an internal wiring material that performs the signal transfer in the cellular phones, high repeated bending resistance is required.
In order to cope with these requirements, an micro coaxial cable is used as the internal wiring material that performs the signal transfer in the cellular phones. The micro coaxial cable includes: a center conductor that enables the transfer of the signal; an insulator that is made of a resin composition and covers a periphery of the center conductor; an external conductor that serves as a shield and covers a periphery of the insulator; and a jacket that covers a periphery of the external conductor.
In order to connect the micro coaxial cable to a connector, as shown in FIG. 2, it is necessary to expose tips of the center conductor 3, the insulator 105 and the external conductor 8 by predetermined lengths. In the case of a usual cable, such tip exposure is performed by a mechanical method of cutting the cable by using a rotary blade or a chemical method of exposing the tips by using an etching material. However, when a wire diameter is small as in the micro coaxial cable, it is difficult to expose the tip of the center conductor 3 in accordance with such a conventional method. Therefore, by using laser beams, the tips of the center conductor 3, the insulator 105 and the external conductor 8 are exposed. For example, at the time of cutting the jacket 9 and the insulator 105, a CO2 laser (λ=10.6 μm) with a long wavelength is used, and at the time of cutting the external conductor 8 and the center conductor 3, a YAG laser (λ=1065 nn) or an SHG laser (λ=530 nm), which has a short wavelength, is used.
However, when the external conductor 8 is attempted to be cut by irradiating the laser beam onto the micro coaxial cable 101, then as shown in FIG. 3, the laser beam sometimes enters an inside of the coaxial cable from gaps among strands of the external conductors 8. In the case where the insulator 105 is transparent, the laser beam 105 transmits through the insulator 105, and damages the center conductor 3. In the case where the insulator 105 is a material likely to absorb the laser beam, the insulator 105 is burnt and damaged. Moreover, at the time of irradiating the laser beam onto the micro coaxial cable 101, then as shown in FIG. 4, a few strands of the external conductor 8 are cut to expose a part of the insulator 105 in some case. The laser beam is not irradiated onto the external conductor 8 only once but irradiated thereonto several times. Accordingly, when the laser beam is irradiated again after a part of the insulator 105 is damaged, even the center conductor 3 is damaged.
Therefore, an micro coaxial cable has been required, which does not cause damage on the insulator 105 or the center conductor 3 at the time of cutting the external conductor 8 of the micro coaxial cable concerned by the YAG laser or the like.
As means for solving the above-described problem, in Patent Literature 1, it is described that carbon black is added into the resin composition that composes the insulator. However, there has been room for improvement against inferiority in withstand voltage properties.